I. Field of the Invention
The present invention relates to a level sensor mounting.
II. Description of Related Art
Typically automotive fuel systems use a rotary resistive fuel level sensor that is mounted directly to the fuel pump module to measure remaining fuel inside the tank.
The fuel tank is becoming more complex as many OEM's are packaging other components such as batteries, exhaust and driveline components around or through the fuel tank. A major advantage of a plastic fuel tank is it offers car manufacturers the ability to optimize and utilize available vehicle environment for fuel storage. However, because of this advancement many fuel systems are being designed with pump modules which are located below the full fuel level. This is known as a wet pump mounting. Wet mountings often inhibit the rotary fuel level sensor from sweeping to the full stop fuel level. Improving the measurement range requires a longer sensor float arm rod or an extension bracket to reposition or extend the sensor mounting off of the pump module. This can increase the difficulty of installing the pump module assembly inside the tank and can also decrease the accuracy of the measurement. Often it is not possible to reach the optimum sweep for the rotary fuel level sensor float arm even with an extension.
Other issues related to resistive rotary fuel level sensors are damage to the resistive circuit card due to aggressive fuels, limited resolution, and wear or damage of moving parts.
Because of these issues, car manufactures prefer to have a fuel level sensor with no moving parts.
Although many technologies have existed which have no moving parts, the cost has typically been two to five times higher than a resistive rotary gage. Introduction of non-moving part fuel level sensors for production applications has been limited to specialty vehicles due to high cost.
Another issue with some non-moving part fuel level sensors is that they are not bottom referenced (meaning they cannot measure to the bottom, empty level of the fuel tank) because they are usually only fixed to the top of the fuel tank, and not to the bottom.
For instance, U.S. Pat. No. 4,679,431 teaches the fixation of a capacitance fuel level sensor to the top of the tank only, using a specific, rather complicated system with a plurality of discs.
The problem of poor measuring accuracy owed to the lack of bottom referencing was already addressed in document FR 2,560,167, which solves the problem with a fixing method through which the gauge extends outside the tank which is nowadays avoided for permeability (environmental) reasons.